1. Field of the Invention
The present invention is related to an improved power supply in systems having two or more power input lines for redundancy.
2. Description of the Related Art
Mission critical systems are often designed to withstand a single point of failure, such as a power failure from a single power source. The term “power source” refers to the source of electrical power (Le., alternating current (“AC”) power or AC power signal), which may be, for example, a power utility such as Pacific Gas & Electric or Southern California Edison. A power failure may be caused by a variety of reasons. For example, a power failure may be caused by bad weather, crumbling infrastructure, or power over load, as well as a variety of other reasons.
Systems, such as mission critical systems, which have two or more power cords for redundancy are often referred to as redundant systems. A power cord connects a redundant system to a device (e.g., a power strip, a power outlet, etc.) through which an AC power signal or AC power signals may be received at the redundant system In particular, the AC power entering certain systems (e.g., a personal computer (PC) or workstation) may be described as an AC power signal over each power input line, while AC power entering certain other systems may be described as AC power signals over each power input line (since these systems use “3-phase” power).
Redundancy refers to use of multiple systems, such that when a first system fails, another system may take over the functionality of the first system. Any computing device, such as a server, mainframe, storage system, router, etc., may be a redundant system or may be part of a redundant system. For example, all powered devices in a server room of a service provider (e.g., a financial institution) may be a redundant system.
In a system in which two or more power cords are used for redundancy, having all of the power cords inadvertently plugged into the same power source can jeopardize the redundancy of the redundant system FIG. 1 illustrates an example of an erroneous power set-up that eliminates the redundancy of computer system 100. Computer system 100 was designed to be a redundant system with power supplies 120 and 130. Power supplies 120 and 130 are within a redundant system and convert an AC power signal to a direct current (“DC”) power signal. In this example, an electric company is the power utility 150 that provides electrical power to both power supplies 120 and 130 via a power strip 140. By using the same power utility 150 for both power supplies 120 and 130, a power failure at the electric company that is the power utility 150 will bring down computer system 100. On the other hand, if power supplies 120 and 130 were powered by separate power utilities, then the computer system 100 would continue to be powered by the second power utility in the event of a failure by the first power utility.
Often, redundant systems are powered by an uninterruptible power supply (“UPS”). A UPS includes a battery pack power source and typically receives an AC power signal from a power utility. After a power outage at a redundant system, a UPS enables data to be saved prior to shut down. That is, a UPS provides backup power, via battery, when the electrical power fails or drops to an unacceptable voltage level. There are several types of UPS systems available today including an “online UPS,” a “standby UPS,” and a “line interactive UPS.” An online UPS provides a constant source of electrical power from a battery, while the batteries are being recharged from AC power. A standby UPS, also called an “offline UPS,” normally draws current from an AC outlet and switches to battery power within a few milliseconds after detecting a power failure. A line interactive UPS is a hybrid of the online and standby UPS systems.
All UPS systems switch to battery power when the AC power fails. The different types of UPS systems handle the power differently under normal conditions. Standby UPS systems provide limited attenuation, whereas line interactive UPS systems will adjust the voltage and smooth out bad harmonics. Additionally, online UPS systems are constantly regenerating clean power.
Currently available UPS systems receive an AC power signal from a power utility and supply the AC power signal over a power cord and a status signal over a data line (e.g., a serial cable) to a device (e.g., a redundant system) being powered. The status signal may include information about an AC failure and the remaining power capacity (e.g., in minutes) of the UPS. For example, the status signal may indicate an AC power signal failure and that the UPS can continue to provide power for another 53 minutes. The status signal may continue to provide updates on the capacity until the UPS has zero capacity left and stops providing power.
Redundant systems with two power cords should be connected to independent and separate power sources. Since each UPS system supplies an AC power signal to a device, such as a redundant system, each UPS system may be considered to be a power source. For example, connecting each power cord of a redundant system to different UPS systems provides independent power sources to the redundant system (even if both UPS systems receive electrical power from the same power utility). Also, the first power cord may be connected to a UPS system, while the second power cord is plugged into an electrical output powered by a power utility. Alternatively, each power cord can be powered by different power utilities.
FIG. 2 illustrates an example of computer systems 270 and 280 incorrectly connected to two different UPS modules 250 and 260. A UPS module 250 receives an AC power signal at input 251, and UPS module 260 receives an AC power signal at input 261. In this example, the set-up is erroneous because each UPS system sends a power signal and a status signal over separate lines, and the data line of each UPS system has been inadvertently plugged into a device not powered by that UPS system. In particular, a UPS module 250 provides an AC power signal to a power supply 210 over power cord 252 and a status signal to a serial port 240 over data line 253. A UPS module 260 provides an AC power signal to a power supply 220 over power cord 263 and a status signal to a serial port 230 over data line 262. In this situation, the computer systems 270 and 280 think the status signal coming from UPS 250 is associated with UPS 260 and the status signal coming from UPS 260 is associated with UPS 250. The computer systems 270 and 280 do not have the intelligence to know that the data lines were incorrectly plugged into the wrong ports.
FIG. 3 illustrates another possible erroneous set-up. In FIG. 3, computer system 300 receives power from the same power utility 380 by connecting power cords 371 and 372 to power strip 370. Power cord 371 provides an AC power signal to a power supply 310 and power cord 372 provides an AC power signal to power supply 320. UPS 350 receives an AC power signal 351 and provides a status signal over a data line 352 to a port 330. UPS 360 receives an AC power signal 361 and provides a status signal over a data line 362 to a port 340. In this situation, the computer system 300 thinks that the status signal from data line 352 is associated with the AC power signal from power cord 371 and that the status signal from data line 362 is associated with the AC power signal from power cord 372. The computer system 300 does not have the intelligence to know that the status signals are not associated with the power signals coming from power cords 371 and 372, respectively. Furthermore, the computer system 300 thinks it can still withstand a single power failure, but, in reality, computer system 300 cannot withstand any power failures.
The examples described above illustrate only a few ways in which a redundant system can be incorrectly set-up. It is therefore desirable to have the redundant system automatically and reliably determine that its power sources are truly distinct or independent.